In recent years, there have been developed hydraulic shovels that accumulate in accumulators positional energy of a working unit and that enable the accumulated positional energy to be reused for a lift operation and the like of a working machine. In this case, in order to accumulate sufficient positional energy, a plurality of accumulators having large capacities need to be installed. Further, an accumulator arrangement space needs to be secured on a hydraulic shovel slewing frame, and a structure (the slewing frame) design that can bear the weight of the accumulators is demanded.
On the other hand, because of the structure of the hydraulic shovel, heavy goods are desired to be arranged at the back of the vehicle. Therefore, at present, there is employed a design for providing the accumulator arrangement space in front of a rear-end part counterweight on the slewing frame, and reinforcing the periphery of the accumulator fitting portion based on the weight of the accumulators.
As techniques for solving the above problem, techniques for using the internal space of the counterweight for the arrangement of the accumulators are disclosed (see Patent Document 1 and Patent Document 2, for example).
Patent Document 1 indicates that, in a hydraulic shovel that includes a counterweight detachable device, accumulators are arranged inside a counterweight, and a check valve is provided on the accumulator installation base at the counterweight side. With this arrangement, in case of separating the counterweight from a machine body at a transportation time and the like, the counterweight can be separated in a state where the accumulators are left in the counterweight.
Patent Document 2 indicates that as an example of a working machine that can satisfactorily keep stability without increasing the weight of the counterweight, even when the accumulators are in a state of being fitted, the accumulators are arranged on an upper surface of or inside the counterweight.
As advantages of these techniques, when the accumulators play the role of the counterweight, the weight of the counterweight itself can be reduced. That is, the quantity of cement or the like that is filled in the counterweight can be reduced. Further, because the total weight of the counterweight and the accumulator does not increase, it is not necessary to arrange specific reinforcement at the periphery of the slewing frame accumulator fitting portion. Also, the techniques become advantageous in the aspect of layout on the slewing frame.
Patent Document 1: Japanese Patent Application Laid-open No. 2008-45365
Patent Document 2: Japanese Patent Application Laid-open No. 2004-116676